1. Field of the Invention
The present invention relates to a method of manufacturing a glass substrate for an information recording medium (hereinafier, may simply referred to as “glass substrate”), in which at least one of an inner peripheral edge surface and an outer peripheral edge surface has a chamfered shape.
2. Description of the Related Art
A generally called “hard disk” is used as an information recording medium capable of writing and reading a large volume of information at a high speed, and as a substrate used of the hard disk, a glass substrate superior in evenness, hardness and the like has been more often used in recent years in place of a conventional aluminum substrate. FIG. 1 shows respective steps in a conventional method of manufacturing the glass substrate (for example, U.S. Publication 2003/0134734).
First, a glass material is melted (glass melting step), and the molten glass is cast into a lower die and pressed by an upper die to be molded (press-molding step). In the press-molding step, a method shown in FIG. 2 is generally adopted. As shown in FIGS. 2(a)-(c), molten glass 3 is press-molded in a predetermined thickness by an upper die 11 and a lower die 12 comprising a molding surface having a plane shape. For reference, an outer diameter regulating frame having a ring shape for regulating an outer diameter of the glass substrate may be interposed between the upper die and the lower die so as to regulate an outer diameter of a molded glass substrate precursor 13.
The press-molded glass substrate precursor 13 is crystallized or annealed and cooled down (crystallizing step or annealing step). In the cooled-down glass substrate precursor 13, a hole is formed at a central part thereof, if necessary, by a core drill or the like (coring step). Then, in a first lapping step, both surfaces of the glass substrate are lapped so that a general shape of the glass substrate, that is parallelism, flatness, and thickness of the glass substrate, is preliminarily adjusted. Next, an outer peripheral edge surface and an inner peripheral edge surface of the glass substrate are ground and chamfered so that a dimension of the outer diameter and circularity of the glass substrate, a dimension of an inner diameter of the hole, and concentricity between the glass substrate and the hole (inner/outer diameter high-precision processing step) are fine-adjusted. After that, the outer and inner peripheral edge surfaces of the glass substrate are polished so as to remove fine flaws and the like thereon (periphery edge surface polishing step). Next, both surfaces of the glass substrate are lapped again so that the parallelism, flatness and thickness of the glass substrate are fine-adjusted (second lapping process). Then, the both surfaces of the glass substrate are polished so as to remove any undulation on the surfaces (polishing step). The both surfaces of the glass substrate are further polished, if necessary, by an abrasive material having a different grain size (second polishing step). Finally, the glass substrate is washed and examined, and shipped as a glass substrate for hard disk.
As described, according to the conventionally employed method, for example, the two steps, which are the lapping/polishing step and the polishing step, are required for processing the inner and outer peripheral surfaces. As a result, the manufacturing steps are increased, which complicates the overall process and deteriorates a manufacturing efficiency. Further, devices in which the hard disk substrate is installed are increasingly reduced in size and weight, in response to which the diameter of the glass substrate is also being reduced. In order to manufacture the glass substrate having a reduced diameter, however, it is necessary to downsize manufacturing jigs used in the process in comparison to the conventional method, for example, reducing a diameter of the core drill for forming the central hole, as a result of which the work process is complicated. Therefore, the manufacturing efficiency unavoidably deteriorates in the conventional manufacturing method.